As some Internet sites become popular, they may reach a point when a single server may be insufficient to keep up with the load on their system. One solution to such a situation is to combine several servers, also referred to as nodes, into a node group. To clients, the node group, also referred to as a load balancing group, still appears as a single server. Internally, however, workload reaching the node group is distributed evenly among the node group members so that no one node is overwhelmed.
In some network configurations several node groups are created to handle different resources in the system. For example, one node group may be responsible for transferring data files while another node group may handle a site's e-mail service. In addition, some nodes in the network may belong to several node groups, thereby creating overlapping node groups. Although such flexible node group configurations are beneficial because they allow highly efficient resource allocation, they can be difficult to administer.
A network administrator typically configures at least one node in a node group to be a master node, also referred to herein as an lbnode. In general, the master node takes ownership of the node group and is responsible for allocating tasks among the node group members. Thus, in addition to performing the same duties as the other nodes in the node group, the master node is responsible for distributing work among the node group members.
Generally, the master node is manually selected by a network administer. Although the network administrator may use any criteria to select a master node, master nodes are typically selected based on high availability. High availability refers to a node's capacity to provide continuous access to network resources, even when serious network failures occur. Thus, the network administrator is often faced with the task of finding the most highly available node in the node group to select as the group's master node. Finding the most highly available nodes in possibly overlapping node groups may be a difficult undertaking and may require the network administrator to use time-consuming trial and error techniques.
Another method of increasing the availability of a node group is to elect a primary master node and secondary master node, also referred to as a primary lbnode and a secondary lbnode, for the node group. The primary master node actively handles load balancing for the node group, while the secondary master node servers as a backup master node ready to takeover load balancing if the primary master node fails. Creating a master node pair adds redundancy to the node group and, hence, increases the node group's availability. However, adding a secondary master node further complicates matters by requiring the network administrator to now find two nodes in the node group to act as lbnodes. Generally, the primary and secondary lbnodes must still be chosen for maximum availability within a network of possibly overlapping node groups.